Fig 13 - uploaded by Patrick Michel
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Lower panel : the suggested shape of (15) Eunomia is consistent with the strongly asymmetric S-curve obtained for this object. Other possible solutions require the use of other constraints, such as those coming from photometry.
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Thanks to the development of sophisticated numerical codes, a major breakthrough has been achieved in our understanding of
the process involved in small body collisions. Such events play a fundamental role in all the stages of the formation and
evolution of planetary systems, and more particularly of our Solar System. Laboratory experiments on cent...
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Introduction: Most asteroids smaller than 500 km are porous [1]. This porosity may be primordial microporos-ity and/or macroporosity introduced by fragmentation and reaccumulation. Recent work suggests that impacts may have been influential in compacting chondritic precursor materials [2, 3]. To place those results in context requires an understand...
Citations
... The second kind is a pre-fragmented structure, which in addition to incipient cracks, is composed of large undamaged zones, separated by fully damaged particles (seeFig. 3inMichel (2003), for an example). This serves as representing a body that has not suffered any disruption/reaccumulation process yet, but did suffer small impacts that pre-fragmented it. ...
The Veritas family is located in the outer main belt and is named after its apparent largest constituent, Asteroid (490) Veritas. The family age has been estimated by two independent studies to be quite young, around 8 Myr. Therefore, current properties of the family may retain signatures of the catastrophic disruption event that formed the family. In this paper, we report on our investigation of the formation of the Veritas family via numerical simulations of catastrophic disruption of a 140-km-diameter parent body, which was considered to be made of either porous or non-porous material, and a projectile impacting at 3 or 5 km/s with an impact angle of 0° or 45°. Not one of these simulations was able to produce satisfactorily the estimated size distribution of real family members. Based on previous studies devoted to either the dynamics or the spectral properties of the Veritas family, which already treated (490) Veritas as a special object that may be disconnected from the family, we simulated the formation of a family consisting of all members except that asteroid. For that case, the parent body was smaller (112 km in diameter), and we found a remarkable match between the simulation outcome, using a porous parent body, and the real family. Both the size distribution and the velocity dispersion of the real reduced family are very well reproduced. On the other hand, the disruption of a non-porous parent body does not reproduce the observed properties very well. This is consistent with the spectral C-type of family members, which suggests that the parent body was porous and shows the importance of modeling the effect of this porosity in the fragmentation process, even if the largest members are produced by gravitational reaccumulation during the subsequent gravitational phase. As a result of our investigations, we conclude that it is very likely that the Asteroid (490) Veritas and probably several other small members do not belong to the family as originally defined, and that the definition of this family should be revised. Further investigations will be performed to better constrain the definitions and properties of other asteroid families of different types, using the appropriate model of fragmentation. The identification of very young families in turn will continue to serve as a tool to check the validity of numerical models.
... From these characteristics, reproduced recently by numerical simulations (see, e.g. [30] and references therein), it is now established that an asteroid family is the outcome of the disruption of a large asteroid due to an impact with another small asteroid. As a consequence, a large asteroid is transformed into a group of smaller bodies, To be published in: "Small Bodies in Planetary Systems". ...
... Section 3 summarizes the most recent study on the spin limits of small bodies and what the observed spins tell us on the strength and internal structure of these objects. The latest results on the limit distances of small bodies to a planet as a function of their strength are then presented in Section 4. Several reviews have already been devoted to our current understanding of the collisional disruption of small bodies based on numerical simulations (see., e.g., [29], [30]), therefore this problem is briefly discussed in Section 5, concentrating only on the some important issues and open areas. Discussions, conclusions and perspectives are then given in Section 6. ...
... Thus, the use of a strength measure that decreases with size is now a common feature of the studies of disruption of small bodies by impacts (see, e.g. [13], [30]) and has even been demonstrated experimentally ( [19]). A common model for a distribution of incipient flaws in a solid body is a power-law Weibull distribution ( [45]). ...
During their evolutions, the small bodies of our Solar System are affected by several mechanisms which can modify their properties.
While dynamical mechanisms are at the origin of their orbital variations, there are other mechanisms which can change their
shape, spin, and even their size when their strength threshold is reached, resulting in their disruption. Such mechanisms
have been identified and studied, by both analytical and numerical tools. The main mechanisms that can result in the disruption
of a small body are collisional events, tidal perturbations, and spin-ups. However, the efficiency of these mechanisms depends
on the strength of the material constituing the small body, which also plays a role in its possible equilibrium shape. As
it is often believed that most small bodies larger than a few hundreds meters in radius are gravitational aggregates or rubble
piles, i.e., cohesionless bodies, a fluid model is often used to determine their bulk densities, based on their shape and
assuming hydrostatic equilibrium. A representation by a fluid has also been often used to estimate their tidal disruption
(Roche) distance to a planet. However, cohesionless bodies do not behave like fluids. In particular, they are subjected to
different failure criteria depending on the supposed strength model. This chapter presents several important aspects of material
strengths that are believed to be adapted to Solar System small bodies and reviews the most recent studies of the different
mechanisms that can be at the origin of the disruption of these bodies. Our understanding of the complex process of rock failure
is still poor and remains an open area of research. While our knowledge has improved on the disruption mechanisms of small
bodies of our Solar System, there is still a large debate on the appropriate strength models for these bodies. Moreover, material
properties of terrestrial rocks or meteorites are generally used to model small bodies in space, and only space missions to
some of these bodies devoted to precise in situ analysis and sample return will allow us to determine whether those models
are appropriate or need to be revised.
We will discuss some specific applications to the rotation state and the shapes of moderately large asteroids, and techniques
of observations putting some emphasis on the HST/FGS instrument.
